IEC 60034-29:2008 pdf download – Rotating electrical machines – Part 29: Equivalent loading and superposition techniques – Indirect testing to determine temperature rise
Components 1 , 2, and 3 may be, for example, the stator winding, the rotor winding, and the stator iron. In some test conditions, certain losses may be equal to zero, and hence the related term in the equation disappears. For example, using the above assigned subscripts, a synchronous machine has K 1 1 P 1 = 0 at no load and K 1 3 P 3 = 0 at short circuit.
The method is based on the principle that the coefficients K do not change from test to test, i.e. that the cooling conditions are invariable between tests, which requires the speed to be the same in each test. The method is also based on the principle of linear thermal conditions so that temperature rises in one case can be added to those for another case. It requires the losses in the relevant component parts to be known with sufficient accuracy for each case, either by calculation or measurement. When the tests have been completed and the equations compiled, the coefficients K can be derived by simple arithmetic.
These are then used in a final equation with the losses for the rated load condition to calculate the temperature rise of component 1 . By similar means, the temperature rises at rated load of components 2, 3, etc. can be derived. If any component loss is temperature dependent (for example, stator copper loss), then the calculation procedure has to be repeated using values for the loss corrected for the estimated temperature rise. It is normally necessary to do this iteration once only. For the calculation of winding temperature rises corrected to a reference ambient temperature equations in closed form are also provided.
The method may be used to determine the temperature rise of any component at any load if the losses at that load are known. The slope factors of temperature rise (K 1 2 , etc.) may be useful in other thermal modelling studies, for example, in analysing the response to supply unbalance, voltage reduction, etc.
In all superposition tests, correction is necessary for variation in heat exchanger performance (if one is fitted to the machine), as the thermal performance of the heat exchanger will partly depend on the total loss in each test.
5.1.2 Temperature rise When determining the temperature rise values of machine parts by superposition tests, the variations from the results that should be obtained at rated-load test are always to be considered. The uncertainty value γ (%) for rated load is defined:
NOTE 1 The uncertainty values obtained by superposition tests may be negative (test temperature rise is lower than under normal operation) or positive (test temperature rise is larger than under normal operation).
Consequently, for comparing with the temperature rise values given in IEC 60034-1 , test results have to be multiplied with a correction factor σ:
NOTE 2 For negative uncertainty values the correction factor is > 1 .
5.1.3 Estimation of temperature rise from reduced load tests
When estimating the temperature rise from tests at reduced load, the losses should be separated into variable (load) losses and constant (iron, friction and windage) losses. For the adjustment of temperature rise values, the machine may be considered as a two-component system (see 4 0 H 5.1 .1 ).
NOTE Depending on the enclosure and pole number of the machine, the temperature rise due to the constant losses can be significant.
Tests on large machines have shown that the separation of loss components results in better agreement between the reduced load estimation and the full load actual test. When a load test is performed at currents different from rated current, the I²R losses have to be converted to full load with the squared ratio of the currents, and the resistance R has to be corrected for total winding temperature.
